The QD eTPU function set is intended to process signals generated by a shaft encoder in motion control systems. It uses two channels to decode a pair of out-of-phase encoder signals and to produce a 24-bit, bi-directional position counter, together with direction information, for the CPU. Additional input channels can also be processed. The index channel receives a pulse on each revolution. Based on the actual direction, a revolution counter is incremented or decremented on the index pulse. A further additional input channel can indicate a home position. When the position is reached, appropriate actions are taken (reset of the position counter and the revolution counter).
For full description refer to AN2842.